The present invention is related generally to the field of orthodontics. More particularly, the present invention is related to improved systems and methods for removably attaching a dental positioning appliance to the dental features of a patient during orthodontic treatment.
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as xe2x80x9cbraces.xe2x80x9d Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and 0-rings. The brackets and bands are bonded to the patient""s teeth using a suitable material, such as dental adhesive. Once the adhesive has set, the archwire is attached to the brackets by way of slots in the brackets. The archwire links the brackets together and exerts forces on them to move the teeth over time. Twisted wires or elastomeric 0-rings are commonly used to reinforce attachment of the archwire to the brackets. Attachment of the archwire to the brackets is known in the art of orthodontia as xe2x80x9cligationxe2x80x9d and wires used in this procedure are called xe2x80x9cligatures.xe2x80x9d The elastomeric 0-rings are called xe2x80x9cplastics.xe2x80x9d
After the archwire is in place, periodic meetings with the orthodontist are required, during which the patient""s braces will be adjusted. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontist""s office. Moreover, from a patient""s perspective, they are unsightly and uncomfortable. Moreover, the archwire and ligatures which connect the brackets in a continuous network make brushing, flossing between the teeth and other dental hygiene procedures difficult, possibly contributing to the development of gingivitis. Consequently, alternative orthodontic treatments are needed. In particular, it would be desirable to use appliances which can be removed by the patient during daily dental hygiene routines, while participating in athletic activities, or for cosmetic purposes.
A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances comprise a thin shell of elastic material that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually moves the teeth through a series of intermediate configurations to a final desired configuration. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT Publication No. WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
In addition to their ease of use, polymeric positioning appliances are generally transparent, providing an improved cosmetic appearance, and impart substantial force on the teeth, due to stiffness of the appliance. The stiffness of an elastic positioning appliance is a result of the modulus of the thermoformable polymer materials from which it is made. The higher the modulus of the materials, the higher the stiffness of the appliance. When a patient positions such an appliance over a prescribed group of teeth, one or more of the teeth will provide a base or attachment region for holding the positioning appliance in place while the stiffness of the polymeric material will impart a resilient repositioning force against one or a portion of the remaining teeth. By designing the appliance to cover the teeth, a much larger contact surface area is afforded compared to traditional spring retainers and wire-based appliances. However, such attaching and repositioning abilities of removable elastic positioning appliances are still dependent on the physical features and configuration of the patient""s teeth, palette, and previous dental work, to name a few. For example, shell-like elastic polymeric positioning appliances have difficulty applying certain forces to individual teeth, such as extrusive force (e.g. pulling or raising a tooth relative to the jaw).
Attachment devices anchored to one or several teeth can improve repositioning of the teeth with polymeric appliances. Particularly difficult tooth movements are rotations and extrusions. Using appliances with attachment devices can improve tooth rotation and extrusion. However, during treatment, coupling between an appliance and attachment may become disengaged. This disengagement may occur if a tooth does not move as planned, or moves in a planned direction but not as rapidly as planned. If the planned position of the tooth and attachment differs from the actual position of the tooth and attachment, the receptacle for the attachment formed in the polymeric shell may not properly receive the attachment on the tooth. If the receptacle formed in the polymeric shell does not properly receive the attachment, the force applied to the tooth decreases and the treatment outcome may be less than ideal.
Thus, it would be desirable to provide tooth positioners, systems, and methods which apply adequate force in desired directions to selected teeth at specific times during treatment. In particular, it would be desirable to enable the fabrication and use of removable positioners and systems which can apply extrusive, rotational, and other directional forces which have heretofore been difficult to apply with removable positioners. It would also be desirable to reduce the cost of the orthodontic treatment and retain the patient benefits of a removable appliance in cases where they might not otherwise be available. At least some of these objectives will be met by the designs and methods of the present invention described hereinafter.
The present invention provides improved methods and systems for using removable polymeric shell appliances for moving teeth. In particular, the present invention configures and positions a force receiving component on a tooth attachment, typically an anchor bonded to a tooth, and a force applying component on the shell appliance, typically a receptacle formed in a wall of the shell which receives the attachment when the shell is placed over the teeth. The attachment and receptacle will be configured to create an engagement point or region therebetween, where the engagement point or region moves or xe2x80x9cshiftsxe2x80x9d as the teeth are repositioned so that the force transmitted is optimized to promote efficient tooth movement throughout the treatment stage using each particular appliance. In one example, both the force applying and the force receiving surfaces are inclined planes which slide over each other as the tooth is moved so that a desired force is maintained on the tooth. In another example, the further receiving and applying surfaces comprise pawl-and-ratchet structures that permit relative positional adjustment as the tooth is moved. Other examples are described hereinafter.
In a first aspect the invention comprises a method of repositioning teeth. The method comprises bonding an attachment having at least one force receiving component to a preselected position on at least one of the teeth. A provided shell repositioning appliance has at least one force transmitting component for transmitting a force. The polymeric shell repositioning appliance is placeable over the teeth so that the force transmitting component and the force receiving component engage each other at a contact point. The contact point is within a locus of engagement, and a position of the contact point adjusts within the locus of engagement as the tooth is repositioned.
In specific embodiments, the locus of engagement extends over a pre-selected distance. The force receiving component and the force transmitting component are positioned so that the force transmitted to at least one tooth which lags its intended position is increased. The polymeric shell appliance placed over the teeth may include a cavity shaped so that a space between the appliance and the tooth permits the tooth to move into an intended position. The polymeric shell and attachment may be shaped to permit the attachment to move relative to the appliance along a channel as the contact point adjusts position within the locus of engagement. In some embodiments a first pair comprises the force transmitting component and a second pair comprises force receiving component, and each member of each pair are positioned on opposing sides of the tooth.
In many embodiments the pre-selected distance over which the locus of engagement extends is at least about 0.5 mm. The distance may be at least about 1 mm. The force transmitting component and force receiving component may be arranged to rotate at least one of the teeth with the transmitted force. In some embodiments the force transmitting component and force receiving component are arranged to extrude at least one of the teeth with the transmitted force. Alternatively, the force transmitting component and force receiving component may be arranged to intrude at least one of the teeth with the force. The force transmitting component and the force-receiving component may comprise a cam and a follower. In some embodiments the contact point adjusts position within the locus of engagement, and this adjustment establishes an equilibrium as the force transmitted to the at least one tooth which lags its intended position is increased.
The force transmitting and force receiving components may be arranged to counter a force from a first surface with a force from a second surface. In specific embodiments the force from the first surface is an intrusive force and the force from the second surface is an extrusive force. Alternatively, the force from the first surface is an extrusive force and the force from the second surface is an intrusive force. A single attachment device may include a first surface and a second surface that counters a force from the first surface. Alternatively, a first attachment device may comprise the first surface and a second attachment device may comprise the second surface. In specific embodiments, the force transmitting component and the force-receiving component comprise a pawl and a ratchet. The force-transmitting component may comprise the ratchet and the force-receiving component may comprise the pawl. Alternatively, the force-transmitting component may include the pawl and the force-receiving component may include the ratchet. In specific embodiments the force receiving component and the force-transmitting component comprise meshing teeth.
In another aspect the invention comprises a system for repositioning teeth in a patient jaw comprising an attachment for bonding to a tooth at a pre-selected position. The attachment has at least one force receiving component for receiving a force. The system also includes a polymeric shell repositioning appliance placeable over at least some of the teeth in the patient jaw. The appliance has at least one force transmitting component positioned to engage the force receiving component of the attachment when the attachment and the force receiving component engage each other at a contact point. The contact point adjusts a contact position within the locus of engagement as the tooth is repositioned.
In some embodiments the locus of engagement extends over a preselected distance. The force receiving component and the force transmitting component are positioned so that the force transmitted to at least one tooth which lags its intended position is increased. In some embodiments the polymeric shell appliance placed over the teeth includes a cavity shaped so that a space between the appliance and the tooth permits the tooth to move into an intended position. The polymeric shell and attachment are shaped to permit the attachment to move relative to the appliance along a channel as the contact point adjusts position within the locus of engagement. A pair may comprise the force transmitting component and the force receiving component, each member of each pair may be on opposing sides of the tooth.
In many embodiments the pre-selected distance over which the locus of engagement extends is at least about 0.5 mm. The distance may be at least about 1 mm. The force transmitting component and the force receiving component maybe arranged to rotate at least one of the teeth with the force. Alternatively, the force transmitting component and the force receiving component may be arranged to intrude at least one of the teeth with the force. The force transmitting component and the force receiving component may be arranged to extrude at least one of the teeth with the force. The contact point may adjust position within the locus of engagement to establish an equilibrium as the force transmitted to the at least one tooth which lags its intended position is increased.
In some embodiments the force transmitting and force receiving components are arranged to counter a force from a first surface with a force from a second surface. In specific embodiments, the force from the first surface is an intrusive force and the force from the second surface is an extrusive force. Alternatively, the force from the first surface is an extrusive force and the force from the second surface is an intrusive force. A single attachment device may comprise the first surface and the second surface. Alternatively, a first attachment device may comprise the first surface and a second attachment device comprises the second surface.
In further embodiments the force transmitting component and the force-receiving component comprise a pawl and a ratchet. In specific embodiments the force-transmitting component comprises the ratchet and the force-receiving component comprises the pawl. Alternatively, the force-transmitting component comprises the pawl and the force-receiving component comprises the ratchet. In an embodiment, the force receiving component and the force-transmitting component comprise meshing teeth.
In yet another aspect the invention comprises a method for designing a polymeric shell tooth repositioning appliance. The method includes locating an attachment on at least one tooth among several teeth of a model to define at least one force receiving component for receiving a transmitted force. The method also includes positioning an attachment receptacle to define at least one force transmitting component in a polymeric shell placeable over the teeth. The force transmitting and force receiving components are shaped to engage each other at a contact point within a locus of engagement. A position of the contact point adjusts within the locus of engagement as the tooth is repositioned.
In specific embodiments the locus of engagement extends over a preselected distance. The force receiving component and the force transmitting component are positioned so that the force transmitted to at least one tooth which lags its intended position is increased. The polymeric shell appliance placed over the teeth may include a cavity shaped so that a space between the appliance and the tooth permits the tooth to move into an intended position. The polymeric shell and attachment are shaped to permit the attachment to move relative to the appliance along a channel as the contact point adjusts its position within the locus of engagement. A prominence may be placed at the locus of engagement to increase the transmitted force.
In some embodiments the model is a computer model and the attachment is a virtual attachment. Modifying the virtual attachment forms a modified virtual attachment. The modified virtual attachment may be for forming the attachment receptacle in the polymeric shell. The modifying of the virtual attachment may include modifying a position of the virtual attachment. The modified virtual attachment may be similar to a shape of at least a portion of the virtual attachment, for example a similar shape formed by truncating a portion of the virtual attachment. In preferred embodiments, the modifying of the virtual attachment increases the force transmitted by the polymeric shell. The modifying of the virtual attachment may include enhancing a surface detail of the virtual attachment to form a modified virtual attachment having enhanced surface detail.